A wide range of methods and apparatus are known to the art for processing biologically degradable waste products to provide a clarified and safe effluent for return to nature. The attention in recent years focused on deterioration of our ecology has placed high priority on the development of better waste treatment systems than those presently known to this already refined art.
Basically, biological sewage treatment is a process in which microorganisms metabolize waste products producing gaseous and soluble molecular end products, and additional bacterial cells. The rapidity and effectiveness of the process is aided by increasing the quantity of bacterial cells, or standing crop, available to carry out the metabolism. The concentrating and holding of the organisms in the system has in the prior art been obtained by one of several physical or biological techniques including flocculation, sedimentation and provision of large surface areas for bacterial multiplication.
Two widely known and conventional techniques for treating biodegradable waste products are the activated sludge and trickling filter processes. In an activated sludge system, contact of organisms with waste is brought about by mixing sewage with sludge, i.e., a concentrated solid containing flocs of organisms, to form the mixed liquor and then subjecting the mixture to strong agitation while introducing large volumes of air. In trickling filter systems, the biological organisms are not present in or submerged in an aqueous medium but are present in the form of exposed growth on the surface of suitable base objects in contact with the atmosphere and reaction is brought about by flowing the waste in relatively thin streams in direct contact with the biological slimes.
Combination or hybrid systems employing aspects of both the activated sludge and the trickling filter are also known to the art. An example of such a system is disclosed in U.S. Pat. No. 3,563,888. Another example is well-known Hays process which utilized vertically oriented flat asbestos cement plates as the contact surfaces for aerobic microbial growth. Air is blown under the plates through orifices in a base grid to provide the requisite oxygen.
A further and detailed discussion of the prior art processes including the Hays process as well as an extended discussion and analysis of a laboratory study of the method and system of the present invention are provided in a Master of Science thesis entitled "A Fixed Media Complete Mixing Activated Sludge System" by Murli Tolaney submitted to the Department of Civil Engineering and the Faculty of the Graduate School of the University of Kansas, May 1971.